1. Field of the Invention
The invention relates in general to a luminous apparatus, and more particularly to the luminous apparatus capable of adjusting the luminance.
2. Description of the Related Art
In the Age of high technology, scanner has been required in the modern life due to its great functions of scanning the original drafts, such as the pictures, the photos, and documents, and then transforming and saving the image as the digital files. It is a very convenient way for the users to keep or find the original drafts. The structure and the principle of the scanner are described below.
Referring to FIG. 1A, which depicts the diagram of the general flatbed scanner. The scanner 100 has a base 102 and a lid 104, and one end of the lid 104 is attached to one end of the base 102 with a hinge 106, that allows the pivoting of the lid 104 on the base 102. The base 102 includes a chassis 108 and a transparent platform 110, which the chassis 108 is removable situated inside the base 102 in order to capture the image of the original draft 112 step by step.
Referring to FIG. 1B, which depicts the side view of the scanner in FIG. 1A. The chassis 108 includes the light source, the reflector 115, the lens 116, and the photo-electronic sensing device 118. Generally, the light source is a fluorescent lamp 114 with a single tube, which the fluorescent lamp 114 is equipped in the carriage 120 to radiate through the aperture 121 of the carriage 120, and provide the light required for scanning. Additionally, the reflector 115, the lens 116, and the photo-electronic sensing device 118 are all equipped inside the chassis 108. Before scanning the original draft 112, the base 102 have to be covered with the lid 104 to prevent the scanning process from interference by the external light, and the quality of the obtained image won't be affected thereby. During scanning, the light emitted from the fluorescent lamp 114 is reflected by the original drafts 112, and then further reflected by the lens 116 and focused on the photo-electronic sensing device 118 by the lens 116. Afterward, the light signal received by the photo-electronic sensing device 118 is converted into electronic signals, and then produce machine-readable data, which is representative of the image of the original drafts 112. The photo-electronic sensing device 118 can be any device capable of converting the light signal into the electric signal, such as Charged Coupled device (CCD) or Contact Image Device (CIS).
Additionally, the chassis 108 is driven by the stepping motor (not shown in FIG. 1B) to move slightly toward the direction corresponding to the un-scanned area after the light signal is received by the photo-electronic sensing device 118, and then the image of the un-scanned portion of the original draft 112 is captured by the photo-electronic sensing device 118, and further converted into the readable digital data. The above-mentioned steps are performed repeatedly until the original draft 112 is entirely scanned.
Referring to FIG. 1C, which is the sketch of the optical path between the original draft and the fluorescent lamp in the carriage. Usually, fluorescent lamp is a lamp that produces visible light by fluorescence, especially a glass tube whose inner wall is coated with a material that fluoresces when an electrical current causes a vapor within the tube to discharge electrons. Therefore, In FIG. 1C the fluorescent lamp 114 can produces visible light after the two end of the fluorescent lamp are electrified. In order to make the light beams from fluorescent lamp 114 effectively project on the original draft 112 along the direction of the arrow 150, the manufacturer commonly attaches a reflective film 122 in the inner side of the carriage 120,so that the light could be reflected by the reflective film 122 and then effectively projects on the original draft 112 through the aperture 121. However, the light intensity from the lamp varies both spatially and temporally along the length of the lamp, which means the light intensity close to the middle of the fluorescent lamp 114 is stronger than the two ends, so that the light projected on the original draft 112 are not even, and hence the light reflected by the original draft 112 are not even, either. In other words, the luminance of the surface of the original draft 112 is not uniform.
Referring to FIG. 1D, which depicts the top view of the original draft and the fluorescent lamp of FIG. 1C. In FIG. 1D, the fluorescent lamp 114 is M in length, and the original draft 112 is N in length, N is usually smaller than M. The light emitted from the middle part of the fluorescent lamp 114 in stronger than the two ends, so that the luminance of point A of the original draft 112 is higher than points B and C while the light radiates along the direction of arrow 150. Such variation degrades the accuracy of scanned images.
To solve this problem, the reflective film 122 is further improved by the manufacturers, as shown in FIGS. 1E and 1F. FIG. 1E illustrates the carriage with the improved reflective film, and FIG. 1F illustrates the carriage of FIG. 1E is unrolled. For decreasing the intensity of the light, the light cutoff 130a and 130b are pasted up on the two edges of the reflective film 122, respectively. The light emitted from the fluorescent lamp 114 is reflected by the reflective film 122 through the light cutoff 130a and 130b, and consequently projected on the original draft 112 uniformly.
On the other hand, the luminance of the original draft 112 is also related to the light source. Generally, the light intensity of the single-tube fluorescent lamp is not enough, and the quality of scanned images could be degraded. But using the double-tubes fluorescent lamp make the scanner become bulky, and it is also difficult to control the luminance of the original draft 112. Additionally, if using a luminescent apparatus with high-brightness as the light source of the scanner, such as electroluminescent element, the light with strong intensity need to undergo the action of light cutoff for making the luminance of the original draft 112 uniform; however, the luminance of the original draft 112 is still affected due to the diffusion of the light.